style: Apply nixpkgs-fmt and fix

Apply standard formatting and some statix conventions using;

```sh
nixpkgs-fmt **.nix && statix fix .
```

With the intent of making contribution a bit easier and reducing mental
load in hand formatting (in the same vein as [black]).

[black]: https://github.com/psf/black#the-uncompromising-code-formatter

default.nix

@@ -14,8 +14,9 @@ let
       };
     };
   };
-in {
-  types = types;
+in
+{
+  inherit types;
   create = cfg: types.diskoLib.create (eval cfg).config.devices;
   createScript = cfg: pkgs: pkgs.writeScript "disko-create" ''
     #!/usr/bin/env bash